Lisa Marie Presley's Slim-Down: I'm at My Teenage Weight

Like millions of women, Lisa Marie Presley has tried fad diets over the years – with mixed results. Recently spotted in Australia looking slim, the singer-songwriter has finally discovered what works.

"Eating clean and organic is best," Presley, 46, tells PEOPLE from Down Under, where she and her husband, guitarist Michael Lockwood, are touring in support of her album Storm & Grace.

The daughter of the late Elvis Presley sticks to vegetables, chicken, fish, nuts, fruit, almond milk and freshly made juices. Currently at her "happy" weight, she also walks 30 minutes every other day and lifts light weights, usually with Lockwood, her husband of eight years.

It's all paid off: "I'm at the weight I was at when I was a teenager," Presley tells PEOPLE. "I love the way clothes fit right now."

In addition to watching how much she consumes – "I eat half of what I am given, especially when I have carbs or grains," she explains – Presley also makes better choices overall.

"I just had avocado with feta cheese on toast with some spinach," she says. "Last night I had vegetable chicken curry. I watch the rice, obviously. I'll have a fistful."

Presley took a good look at her health a few years ago. "Knowing my family history – my father's side is totally not healthy and they have shorter life spans [her father died at 42], while my mom's side is super fit with long life spans – I didn't know where I would land. So I said, 'Okay. I'm going to play it safe and try to be as healthy as I can be.' "

She decided to make health a priority when she went on tour in 2012. "Being on the road for a three-month run gets intense. I can be really, super disciplined, but I can also be really not disciplined," she says, laughing. "I love Mexican food. So we have to watch that. I'll have one chicken taco."

Presley admits that touring also makes it tough to fit in regular workouts. "I can't always get off the bus and walk for 30 minutes. But the show is 90 minutes long and I'm constantly moving and my adrenaline is pumping, so I'm sure that is burning calories."

While touring is good for her waistline, so is running after her 5-year-old fraternal twins with Lockwood, Harper and Finley.

"The twins are with me on tour and are constantly on the go, so they keep me moving," she says. "I do chase after them, but it's not just that. There's always so much going on with the little ones and the older ones, too [daughter Riley, 24, and son Benjamin, 21, from her first marriage to Danny Keough]. It's a lot!"